It is well known that electrical signals occurring within electronic packages, such as micro-processors, emit electromagnetic energy from the package, which can produce electromagnetic interference (EMI) undesirably affecting other electronic signals in nearby equipment. It is believed that the electrical sockets in which the packages are positioned also emit EMI as the signals from or to the electronic packages pass through the sockets. The amount of radiation being emitted from the sockets, if any, is as yet unknown, and further is expected to vary from one socket construction to another. It is desirable to provide a shield against such emission of EMI, and attempts at EMI shielding in general are well known.
In this connection, it is known to shield signal wires (e.g. U.S. Pat. No. 3,775,552 to Schumacher); to shield signal contact elements in two-piece connector systems (e.g., U.S. Pat. Nos. 4,846,727 to Glover et al. and 4,867,690 to Chumma); and to make connector-encompassing hoods of a shielding material as disclosed in U.S. Pat. No. 4,822,286 to Bionco.
It is further known from U.S. Pat. No. 5,030,115 to Regnier et al. to provide an elongated ground shield across the back faces of a pair of SIMM sockets stacked on top of each other in a socket carrier, and further to insert the shield across the back faces of and between two pair of SIMM sockets stacked in a carrier with each pair facing in an opposite direction. The shield prevents electrical interference being radiating from or received by the terminals of the SIMM sockets.
Disclosed in U.S. Pat. No. Re. 32,370 is a cover for a socket having arms, and having prying tabs on the arms and on depending members that lock the cover to the socket.
U.S. Pat. No. 4,716,494 discloses a spring clip whose latch sections are latched under latch projections.
In the above-identified two copending applications it is proposed to provide a shielding device adapted to be placed around the socket on which an electronic package is positioned, to suppress EMI emissions and further to ground a heat sink retained on the electronic package and thus prevent it from acting as an EMI antenna. However, the systems disclosed in those applications possesses limitations in some respects, particularly from the viewpoints of effectiveness of shielding, ease of assembly and disassembly, and commercial packaging of the shield and socket.
More particularly, shielding systems disclosed in these copending applications use a rectangular socket the peripheral portions of which are planar, except for latching detents provided to secure the latch means of heat-sink retainers, which are secured at one end to a covering heat sink and at their other ends to the latching detents. The shielding device used in those systems is an electrically-conductive frame which surrounds the socket and which has integral grounding or solder tails which extend from its bottom end; it also uses integral, heat-sink contacting, resilient tabs which extend outwardly from the frame to contact skirts which depend from two sides of the heat sink.
While operative for its intended purposes, such systems have some drawbacks. The frame is not securely attached to anything, and thus constitutes a separate and rather fragile piece which may be lost or damaged during storage, packaging, shipping, sale or assembly, and requires assembly by the customer. Further, in order to permit the heat-sink retainers to access the latching detents in the edges of the socket, the frame is cut out at the positions of the latching detents; these cut-outs tend to reduce the effectiveness of the EMI shielding effect. In addition, in order to leave the latching means clear for latching and delatching, the skirts of the thermally and electrically conductive heat sink depend from the sink downwardly on only two sides of the socket, namely those two sides not containing the latching detents, and this also tends to decrease the effectiveness of EMI shielding from what might otherwise be attainable if the skirts completely surrounded the electronic package on all sides.
The objects of the present invention therefore include providing a shielding device adapted to be secured to the socket, and which need not be cut out to accommodate the latch means; providing a socket which will mount and secure the shielding device, and which will cooperate in securing the heat-sink retainer means without requiring cut-outs in the shielding device; providing a heat sink which will permit the heat-sink retainer means to extend through the body of the heat-sink to the latching detents, without having to pass through the walls of the shielding device; and providing depending skirts on the heat sink which extend entirely around the socket, thus enhancing the EMI shielding. Other objects are to provide a socket structure which will support and protect the shielding device, and which will enable easy unlatching of the sink retainer means and removal of the shielding device, when desired, by application of a simple tool applied from above.